CHROMiX ColorNews Issue #17 - Delta-E: The Color Difference

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Welcome to ColorNews, a periodic update on things related to Color Management. We are striving for a regular consistent newsletter of high value to our customers. Please let us know what your interests are so we can address these concerns in our coming issues.

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C H R O M i X C O L O R N E W S

Issue #17
February 18th, 2005

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Quick Notes of Interest:

** CHROMiX is announcing the new Price Guarantee program. See details below.

** The new CHROMiX ColorForums are proving to be a useful support service according to polled users. If you have a technical question or would like to discuss a topic, give it a try! See ColorForums.com or below for more information.

Since our last ColorNews Issue #16 (December 22nd, 2004) here are some of the 'happenings' at CHROMiX worth mentioning:

CHROMiX is proud to announce that we are recently certified to install and train on several popular RIP and other software products including Onyx, EFI Colorproof XF and Caldera. We also sell ColorBurst RIP, GretagMacbeth ProfileMaker, Monaco Profiler, ColorThink (of course!) and several others - and provide consulting for them as well! Give us a call to discuss your needs.

CHROMiX has instituted a new policy that all of our customers will appreciate. Drum roll please..... 'CHROMiX ColorGear will now match any legitimate price from any legitimate competitor on any product we sell'. Even though our pricing has always been considered aggressive (or even the best overall value), there are competitors around who sell on price only but don't support the product or provide anything pre-sales or post-sales. We feel very strongly about providing the highest quality pre-sales and post-sales support you need, and will never change that. Now there's assurance that you will get the best price as well as our great support. There will be a mention on the website stating this policy publicly.

We are excited to announce a new working relationship with eVolve, a great Seattle-based training group. eVolve has the people, skills and experience we've been looking for in a training partner and we expect to work with them to offer their customers and our customers effective color management training in the classroom setting. Keep an eye on our website and theirs for more details of classes to come including the advanced color training you've been requesting.

This is the second month of operation for the CHROMiX ColorForums. We would like to thank everyone who has contributed. We're continuing to improve and refine the usability of ColorForums, and your comments are always appreciated.
ColorForums.com is the first full-featured online forum dedicated to color management tools, techniques, and support. Not only is there a clear web-based interface to all forum topic areas, but it is backed up with a comprehensive email system. You can read and post messages via the web or email, so those of you who don't always have time to surf the web can have the color management community come to you. So visit ColorForums when you have questions or just want to discuss color management.

Because of significant interest and positive customer feedback, we thought it would be helpful to post this again: Steve Upton is the featured speaker in a free QuickTime-based seminar sponsored by Apple and GretagMacbeth. You can find it here (free registration required):. It is part of Apple's Color site, which is worth getting to know:

Many customers mentioned strong interest in the X-Rite DTP-70 spectrophotometer to us because of its blinding speed, only to be idled in the slow lane by not being available. However, the DTP-70 is now shipping in limited quantities and it is living up to it's early reputation. Give CHROMiX Sales a call if you're interested in this great device - 866-CHROMiX Extension 1 or email sales(at)chromix.com for more information.

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Color, Product & Industry News

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Effective January 1st, 2005, X-Rite lowered the prices of the popular Monaco Optix XR and Monaco Optix XR Pro by $50 each. Citing streamlined manufacturing efficiencies, the move effectively keeps the prices at the 2004 prices after applying a $50 rebate. The new list is $249 and $379 respectively. CHROMiX sells these for $219 and $349 respectively.

The WMU Profiling Review 2005 is out and worth checking out. The Review from Dr. Abhay Sharma at Western Michigan University is a consumer report of ICC profile making software and covers all major vendors including GretagMacbeth ProfileMaker 5, MonacoProfiler 4.7, Heidelberg PrintOpen, Pantone Spyder2PRO and many, many others. The WMU Profiling Review 2005 is available via Older versions are free. The latest version has a nominal charge.

If you didn't make the 2004 PIA/GATF Color Management conference in Phoenix, you can buy a CD of the entire conference for $249 ($199 for GATF/PIA members). The CD contains 18 digitally recorded and indexed sessions, including Steve Upton's seminar 'Can You Print or Proof to a Standard?' Download the Order Form from GATF at:

For the first time in nearly 30 years, Pantone has substantially redesigned the Pantone Matching System formula guide. The 2005 formula guide includes color swatches that are nearly 25% larger for increased accuracy and visual reference when specifying and matching colors. The Pantone solid chips book, also redesigned, will provide designers with larger tear-out chips. The 2005 formula guide should set a new benchmark for color. CHROMiX carries Pantone products.

Quark has released a PSD Import plug-in for QuarkXPress 6.5. This long-over due Xtension software allows the import of native Adobe Photoshop files (.psd), with layers, channels, and paths intact, into picture boxes in QuarkXPress layouts. Quark also recently announced QXML (QuarkXPress Markup Language), which is Quark's open-source XML language that works with the standard DOM (Document Object Model).

Kodak announced an agreement to acquire Creo. Creo, which has more than 25,000 customers and offices in 30 countries worldwide, will enhance Kodak with an innovative and progressive digital pre-press product portfolio. Creo has also established significant relationships in the commercial printing industry. If it goes through, Creo's operations will become part of the Graphics Solutions & Services operating unit of Kodak's Graphic Communications Group (GCG). There is a webcast and more information by accessing the Kodak.com investors page at:

Adobe Systems Incorporated announced that leading advertising and branding agencies Ogilvy & Mather, DDB Worldwide, and Wunderman have adopted Adobe InDesign CS software, layout and design program that is a part of the Adobe Creative Suite. One wonders if having strong color management capabilities had anything to do with the decision? Probably.

Adobe has released Camera Raw 2.4 and DNG Converter 2.4 for Mac and Windows.
Camera Raw 2.4, an update to the plug-in for Photoshop CS that enables it to process RAW format files from a variety of digital cameras, adds official support for the Canon EOS 20D, EOS-1Ds Mark II, Powershot S70, Powershot G6 and several models from Konica Minolta.
DNG Converter 2.4 has also been updated to support the same new camera models as Camera Raw 2.4. In addition, it's now possible to embed the entire original RAW format file inside the DNG file, and extract it later if necessary.
Camera Raw 2.4 and DNG Converter 2.4 are available from Adobe's Photoshop downloads page for Mac and Windows at

In 2003, it's estimated that a total of 276 billion pages were printed on narrow format inkjet and color EP printers (defined as 8.5" x 11" pages) according to a report published by I.T. Strategies (editor note, that's over 50 million miles!). They estimate that more than 50% of these pages (152 billion) were printed in color. They go on to say: By 2008, the percentage of color pages should increase to 62% (372 billion pages out of a total of 596 billion). These estimates do not include wide-format inkjet output, which is typically counted in square feet/meters, not pages.

Apple's recent Security Update for OS X 10.3.7 & 10.2.8 had some people curious as to what the ColorSync vulnerability involved was (is).
Here's the answer according to the documentation: Malformed ICC color profiles could overwrite the program heap, resulting in arbitrary code execution. An out-of-specification or improperly embedded ICC color profile could overwrite the program heap and allow arbitrary code execution. There are no known exploits for this issue. With this update, ColorSync will reject incorrectly-formed ICC color profiles.

Speaking of ColorSync....
Here's a reported possible bug: After system re-boot (Mac OS X 10.3.5 + latest updates) a custom monitor profile is not always automatically recognized. It's also reported that sometimes the profile doesn't appear if 'show profiles for this display only' is checked.
To manually solve this, open Displays and choose the profile from the list each time after re-boot. A better suggestion is to upgrade to 10.3.7 which should solve the problem altogether.

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SHOWS & EVENTS

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February 6 - May 15, 2005, Rob Galbraith is doing a 10-city seminar series entitled 'Just Show Me How Pro Tour'. The course is designed for Photographers who make a living with a digital SLR camera, and want to learn more about how to import, select, edit, archive and distribute their work. Price is $149 for a full-day. Register at .

February 20 - 23, PMA 2005 and DIMA 2005 Orlando, FL at the Orange County Convention Center in Orlando, Florida. For more information:

March 17-19, 2005 Graphic Arts 2005. Charlotte Convention Center, NC. This recent trade show and conference brings in thousands of industry professionals from the Southern USA. View many highlights of the 2003 show and sign up to be reminded of the next show in Charlotte, NC.

September 9-15, 2005 PRINT '05 at McCormick Place Complex, Chicago, IL Because of its mammoth size and international presence, PRINT occurs only once every four years and will take the place of GRAPH EXPO and CONVERTING EXPO in 2005.

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ColorFAQ - Delta-E - the color difference

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Each issue, our President Steve Upton will take time to answer questions we receive on a regular basis. If you have specific questions or comments, please see below for how to make submissions.

Delta-E - the color difference

You don't have to spend too long in the color management world before you come across the term Delta-E. As with many things color, it seems simple to understand at first, yet the closer you look, the more elusive it gets.

First, the term itself is confusing. It refers to the difference between colors, and if you're trying to matching colors this is considered an error. Delta means difference or change and E stands for error. So does that mean delta-E means change in error? no... just error... strange...

Anyway, what delta-E (dE) IS, is a single number that represents the 'distance' between two colors. The idea is that a dE of 1.0 is the smallest color difference the human eye can see. So any dE less than 1.0 is imperceptible (as in turn the lights off and head to the pub) and it stands to reason that any dE greater than 1.0 is noticeable (as in put the coffee on, we're going to be here a while). Unfortunately - and probably not surprisingly - it's not that simple. Some color differences greater than 1 are perfectly acceptable, maybe even unnoticeable. Also, the same dE color difference between two yellows and two blues may not look like the same difference to the eye and there are other places where it can fall down.

It's perfectly understandable that we would want to have a system to show errors. After all, we've spent the money on the instruments, shouldn't we get numbers from them? Delta-E numbers can be used for:

- how far off is a print or proof from the original
- how much has a device drifted
- how effective is a particular profile for printing or proofing
- removes subjectivity (as much as possible)

Delta-E 1976

So, a bit of history is probably in order. The L*a*b* colorspace was devised in 1976 (let's just call it Lab for short) and, at the same time delta-E 1976 (dE76) came into being. If you can imagine attaching a string to a color point in 3D Lab space, dE76 describes the sphere that is described by all the possible directions you could pull the string. If you hear people speak of just plain 'delta-E' they are probably referring to dE76. It is also known as dE-Lab and dE-ab (although I'm REALLY not fond of dE-ab as it implies that only the a* and b* color components are calculated and L* is left out)

One problem with dE76 is that Lab itself is not 'perceptually uniform' as its creators had intended. So different amounts of visual color shift in different color areas of Lab might have the same dE76 number. Conversely, the same amount of color shift might result in different dE76 values. Another issue is that the eye is most sensitive to hue differences, then chroma and finally lightness and dE76 does not take this into account (since Lab does not take this into account).

Difference vs Tolerance: if difference is a number showing how 'far apart' two colors are, tolerance is the meaning of the number. Setting a tolerance level (such as 2.0 dE76) defines what you will accept and what you will reject(reproduction tolerance). The available differencing equations will also produce different shaped 'tolerance regions'.

Delta-Lab and Delta-LCH

One type of difference calculation that some people use is delta-L, delta-a, delta-b (dLab). By breaking the error into its components you can sometimes get a feel for what might be causing the error. If the tolerance region for dE76 is described as a round sphere, then dLab is a square cube.

My favorite variation on this idea is delta-LCH. Remember that LCH is Lightness (the same one as in Lab), Chroma (the distance out from the neutral axis - saturation) and Hue (the angle/direction in the 360 degree range). If d-Lab is a box-shaped region then d-LCH is a wedge - like cutting a piece of a flat round ring or washer. The interesting thing about d-LCH is what it can tell you about inkjet behavior. Different LCH values can refer to different problems, for instance:
- larger dL may be a paper difference
- larger dC may be paper coating difference
- larger dH may be an ink difference

As the eye's sensitivity to hue, chroma, and then lightness differ, the tolerance region around each color that contains acceptable color matches is best represented by an rugby ball-shaped ellipsoid. The more modern color difference formulae use this ellipsoid shape and allow you, the user, to vary several different parameters to tune the numbers to match visual comparisons.

CMC l:c

In 1984 the CMC (Colour Measurement Committee of the Society of Dyes and Colourists of Great Britain) developed and adopted an equation based on LCH numbers. Intended for the textiles industry, CMC l:c allows the setting of lightness (l) and chroma (c) factors. As the eye is more sensitive to chroma, the default ratio for l:c is 2:1 allowing for 2x the difference in lightness than chroma (numbers). There is also a 'commercial factor' (cf) which allows an overall varying of the size of the tolerance region according to accuracy requirements. A cf=1.0 means that a delta-E CMC value <1.0 is acceptable.

dE94

A technical committee of the CIE (TC 1-29) published an equation in 1995 called CIE94. The equation is similar to CMC but the weighting functions are largely based on RIT/DuPont tolerance data derived from automotive paint experiments where sample surfaces are smooth.
It also has ratios, labeled kL (lightness) and Kc (chroma) and the commercial factor (cf) but these tend to be preset in software and are not often exposed for the user.

dE2000

Delta-E 2000 is the first major revision of the dE94 equation. Unlike dE94, which assumes that L* correctly reflects the perceived differences in lightness, dE2000 varies the weighting of L* depending on where in the lightness range the color falls. dE2000 is still under consideration and does not seem to be widely supported in graphics arts applications.

A few important points about delta-E calculations in general:

- dE calculations are based on colorimetry which means they are illuminant-dependent. Don't try comparing numbers calculated from colors viewed / measured under different illuminants.
- differing dE due to illuminant is metamerism. If colors are 'adapted' to the same white point then you have a metamerism index.

Finally, which equation should be chosen and how should it be used?

- for basic / fast calculations, you can use dE76 but beware of its problems
- for graphics arts use we recommend dE94 and perhaps dE-CMC 2:1
- for textiles use dE-CMC

Choosing the right tolerance (Billmeyer 1970 / 1979)

1. Select a single method of calculation and use it consistently
2. Always specify exactly how the calculations are made
3. Never attempt to convert between color differences calculated by different equations through the use of averaging factors
4. Use calculated color differences only as a first approximation in setting tolerance, until they can be confirmed by visual judgements - in other words, verify all calculations visually
5. Always remember that nobody accepts or rejects color because of numbers - it's the way it looks that counts.

I realize that this article is one of the more technical that I have written but delta-E is one of those topics that is worth understanding, and it can take a little work. I have also simplified the daylights out of some of my explanations. This is intended as an introduction to the concepts and not a detailed reference work.

At the very least, the next time you hear someone spouting off delta-E values you can ask them which delta-E. If there's a long, confused pause then you'll know what you're dealing with.

For more information and the actual equations I suggest you consult the following sources as I did for this article:

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